[Noisebridge-discuss] charging a cap with a xtal?

Johny Radio johnyradio at gmail.com
Thu Sep 12 19:38:57 UTC 2013

On 9/12/2013 10:38 AM, macegr wrote:
> Must you actually charge it with the oscillator, or are you simply 
> attempting to generate a time-dependent voltage on the capacitor?

must actually charge it with the crystal osc, because our challenge is 
to make something with the parts given us by Instructables.com.

> If you're using a TTL oscillator module, it might be outputting a 5V 
> square wave. This would allow you to charge a peak-detector circuit 
> (diode inline to capacitor connected to ground, optional drain 
> resistor) to within maybe 0.6V below VCC. This will be harder if 
> you're trying to connect directly to an oscillator circuit without an 
> output buffer.

ok, i can add a transistor buffer to the xtal output if necessary. I'm 
assuming the resistor will determine the charge time of the cap. Is this 


Johny Radio

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